With the development of the advanced motor control technologies in home appliances, more and more new motor control methods have been proposed to make the home appliance cheaper, more intelligent and smart. Sensorless control is one of the key technologies, which can make motors run without a position sensor, such as a Hall sensor, encoder or etc. It is known to use sensorless control in three phase motor control systems. But three phase motors are not often used in the drains systems of home appliances such as dishwashers and washing machines. Rather, such systems broadly use a U-shape single phase synchronous permanent magnetic motor (U-SPSPM motor). However, sensorless control of a U-SPSPM motor is not commonly used for several reasons.
A U-SPSPM motor, without knowing the magnetic rotor position, cannot be started in a unidirectional rotation because of cogging torque. Moreover, without rotor position information, any realization of the optimal power regulation will be impossible. Usually a sensor, such as a Hall sensor, is used to get the rotor position information. But there are several trade-offs with use of a sensor-based control: (1) associated costs for a sensor and wiring, (2) required space to add the sensor and circuitry, and (3) added energy consumption. Thus, there is a benefit to achieving sensorless control of a U-SPSPM motor without a physical position sensor.
It is known to provide sensorless control of a U-SPSPM motor with only a voltage signal. Only the voltage signal across the motor is used in this method to estimate the rotor position. A problem with this method is that rotor position information is estimable only when the current is equal to zero, i.e., when u=e0, or when the voltage equals a back-electromotive force. Thus, only detecting motor winding voltage cannot provide a maximum output power and the maximum torque. Consequently, the system will be less efficient based on the same motor design or motor capability.